Many documents are known describing methods and processes for the catalytic conversion of (gaseous) hydrocarbonaceous feedstocks, especially methane, natural gas and/or associated gas, into liquid products, especially methanol and liquid hydrocarbons, particularly paraffinic hydrocarbons.
The Fischer-Tropsch process can be used for the conversion of synthesis gas (from hydrocarbonaceous feed stocks) into liquid and/or solid hydrocarbons. Generally, the feed stock (e.g. natural gas, associated gas and/or coal-bed methane, heavy and/or residual oil fractions, coal, biomass) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas). The synthesis gas is then fed into one or more reactors where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into paraffinic compounds ranging from methane to high molecular weight modules comprising up to 200 carbon atoms, or, under particular circumstances, even more. Preferably the amount of C5+ hydrocarbons produced is maximised and the amount of methane and carbon dioxide is minimised.
One object of the present invention is to increase the proportion of C5+ hydrocarbons and/or to reduce the proportion of carbon dioxide and methane produced.
In the Fischer-Tropsch synthesis, a three phase system of gas, liquid and solid is provided—the solid supported catalyst, the reactants and a diluent, if present, and the products. Such three phase systems may be operated, for example, in a packed-bed reactor or in a slurry-bubble reactor.
A slurry-bubble reactor may comprise a continuous phase of liquid with the solid catalyst suspended therein and gaseous reactants flowing as bubbles through the liquid. The relatively fine powder that can suitably be used in a slurry-bubble or fluidised bed reactor generally consists of micron-sized particles.
A packed-bed, or fixed bed, reactor may comprise a packed bed of solid catalyst particles through which there is a flow of gaseous and liquid reactants. In a packed-bed reactor catalyst particles are relatively large and can have different shapes and sizes. For example, in a fixed bed reactor beads, spheres, saddles or the like can be used. Also extrudates, for example with a trilobe shape, can be used in a packed bed reactor. Other possibilities are catalysts applied to a support, e.g. catalysts coated on shavings or pieces of bent wire or bent tape. The catalysts can also be in the form of fixed structures (or arranged packings) such as gauzes, corrugated sheet material which may or may not be perforated with holes, woven or non-woven structures, honeycombs and foams. Some types of packed beds may be referred to as fixed bed, multi-tubular fixed bed, immobilised slurry, trickle flow fixed bed, down-flow trickle flow packed bed, liquid up-flow packed bed, up-flow liquid full fixed bed, etc.
One preferred Fischer-Tropsch catalyst comprises cobalt as its active component. Iron may also be added, although this adds to the cost and complexity of catalyst preparation. Moreover the concentration of the iron in the catalyst can be difficult to control.
One object of the present invention is to reduce the complexity and cost of preparing iron-containing cobalt catalysts and to increase the control of the iron concentration in such catalysts.